1. Field of the Invention
This invention relates to new and useful improvements in pigment dispersions. It relates particularly to the transfer of a pigment from an aqueous pulp or presscake directly into organic vehicles by an operation known to those skilled in the art as flushing.
2. Description of the Prior Art
Historically, organic pigments have been made by coupling in a dilute aqueous slurry, which is then filtered in a filter press to concentrate the pigment. The presscake is either dried to obtain a dry color, or "flushed" to transfer the pigment particles from the aqueous phase to a non-polar oil or resin phase. This assists in keeping pigment particles non-agglomerated and easier to dilute for ultimate use in inks or coatings. Flushing has been carried out for many decades by mixing pigment presscake with suitable types and quantities of "vehicle" which may be an oil, or a solution of resin or resins and other additives in a solvent. In the prior art, the transfer was effected by merely kneading the presscake and vehicle together until substantially all the water has separated. These were generally batch-type operations employing sigma-blade mixers similar to dough mixers or Banbury mixers. Such processes are very energy intensive and labor intensive since the flushers have to be tilted to remove water from time to time as it breaks, i.e., becomes freed of pigment which has transferred to the oil phase. Also, the final paste or dispersion is often extremely viscous and must be removed manually by shoveling or scraping with hoes and other suitable manual tools.
Accordingly, it is a purpose of the instant invention to provide for flushing a pigment which may be carried out continuously and completely automatically.
Some prior art flushing processes are disclosed in the following patents.
______________________________________ U. S. Pat. No. Issue Date Inventor Assignee ______________________________________ 3,980,488 9/14/76 Barrington et al Sherwin-Williams 2,378,786 6/19/45 Osborne Unassigned on Face 2,637,711 5/5/53 Auer Unassigned on Face ______________________________________
U.S. Pat. No. 3,980,488--Barrington et al--Discloses flushing an organic pigment from an aqueous slurry or presscake into a hydrophobic organic vehicle in conventional equipment such as a homogenizer followed by separating the water from the flushed mass of pigment and vehicle. PA0 U.S. Pat. No. 2,378,786--Osborne--Discloses mixing a pigment slurry with oil, passing the mixture through a colloid mill followed by passing through a heat exchanger and dewatering on a heated belt. PA0 U.S. Pat. No. 2,637,711--Auer--Discloses mixing benzidine yellow and water in a pony mixer until a slurry is formed. The slurry is then homomixed for 30 minutes and colloid milled to complete the pigment deflocculation. It is suggested in the patent that a Gaulin homogenizer be employed for dispersion.
In co-pending U.S. Patent Application Ser. No. 109,357, filed Jan. 3, 1980 entitled Flushing process for Pigments a pigment-containing aqueous pulp-organic vehicle mixture is prepared by forcing the aqueous pulp through a conduit and injecting the vehicle into the conduit containing the aqueous pulp. The mixture is then homogenized, subjected to further mixing where necessary or desirable, and transferred to a traveling horizontal perforated surface whereby some of the water drains from the mixture through the perforations. This effectively removes that water which is most easily removed, thus reducing the amount of water which must be removed in subsequent operations. Temperature control is maintained throughout the process through the use of conventional heat exchangers. The mixture is then forced through a cylindrical chamber having defined at one end thereof an axial opening and at least one second opening spaced from said axial opening. The mixture is forced through the chamber and axial opening by a rotating helical surface whereby the product is forced through the axial opening and water is squeezed from the mixture. The water then exits from the chamber through the second opening. The product is then standardized in a conventional container such as a tank by adding the correct amount of additional vehicle to obtain the desired proportion of pigment and vehicle. In order to reduce the amount of vehicle to be added batch-wise in the standardization tank or container, a pre-determined amount of vehicle may be added to the product by injection after it exits from the axial opening of the chamber. This may then be mixed by a suitable mixer prior to transfer to the standardization tank.